The invention relates generally to electronic oscillators and more particularly to audio oscillators for use in integrated circuits.
Electronic oscillators are useful for constructing transducers, timing circuits, signal generators, etc. Integrated circuits are increasingly being designed in an FET (field-effect-transistor) technology, particularly that using MOS (metal-oxide-silicon) devices. Hence, there is a need for reliable oscillator circuitry particularly suited to MOS technology. While it is possible to adapt a crystal oscillator together with a count-down network to provide such a function, this arrangement does not yield a truly sinusoidal output and for many purposes does not provide sufficient control of output amplitude and choice of frequency for many applications. To alleviate these problems, efforts have been made to construct an oscillator which uses switched capacitor techniques. For the most part, these efforts involve the use of an undamped switched capacitor resonator. Thus far, such an approach has not led to an oscillator with performance suited for most precision applications, primarily due to the difficulty in providing accurate control of amplitude and limiting harmonic distortion, while also assuring proper start-up.